(1) Field of the Invention
The present invention relates to an optical device suitably applicable as a wavelength selective optical switch (λ-SW) for switching over optical paths for respective wavelengths as well as optical level adjusting devices (AGEQ: Automatic Gain Equalizer) for equalizing the optical levels associated with respective wavelengths.
(2) Description of the Related Art
In recent years, there have been introduced large-capacity transmission systems in order to cope with rapidly increasing data traffic due to the widespread of the Internet.
Building up of photonic networks including WDM transmission systems interconnected in mesh configuration in the future would enable provision of a plurality of transmission paths. Thereby it would be made possible to effectively utilize the limited transmission capacity by emphatically allotting lines to transmission paths much in demand depending on the time zone. A WDM transmission system can be realized by switching over the transmission paths for respective wavelengths, wherein there would be necessitated wavelength selective optical switches as essential devices.
Further, a long distance WDM transmission system utilizes amplification relays through optical amplifiers, which causes unevenness in the optical levels of respective wavelengths due to the wavelength dependency of the amplifier gain. Optical amplifiers have the property of concentrating the gain to wavelengths with high intensities, thus resulting in increases in the unevenness of optical levels at every passage through the amplifiers. In order to prevent this, it is necessary to uniformize the optical level for wavelength, and optical level adjusting devices capable of adjusting the amount of attenuation for each wavelength are inserted into transmission paths.
FIG. 20 is a schematic view illustrating a first conventional exemplary configuration (refer to Patent Literature 1) of the aforementioned wavelength selective optical switch. In wavelength selective optical switch 910 according to the first conventional exemplary configuration four waveguide-type diffraction gratings (AWG: Arrayed Waveguide Grating) 911 to 914 and an optical switch 919 are combined such that there are configured a 2×2 switch having two input ports and two output ports (an input port 915 and an add port 916 at the input side and an output port 917 and a drop port 918 at the output side).
In the wavelength selective optical switch illustrated in FIG. 20, demultiplexed lights obtained by demultiplexing through two AWGs 911, 912 at the input side are subjected to path through/switching processes by the optical switch 919 and then distributed to either of two multiplexing AWGs 913, 914 at the output side. Namely, the two AWGs 911, 912 are used to demultiplex wavelength-multiplexed light from the two ports 915, 916 at the input side and the other two AWGs 913, 914 out of the four AWGs are used to output the light on paths which are switched over by the optical switch 919 as wavelength-multiplexed light from the two ports 917, 918 at the output side
FIG. 21 is a schematic view illustrating a second conventional exemplary configuration (refer to Patent Literature 2) of the wavelength selective optical switch. In the wavelength selective optical switch 920 illustrated in FIG. 21, input WDM light is directed to a switch 923 through an optical fiber 922 after the wavelength demultiplexing through an AWG 921 and then multiplexed and outputted by the AWG 921 to a port corresponding to an optical fiber 922 which is the switching-destination.
FIG. 22(a) is a schematic view illustrating a conventional exemplary configuration (refer to Patent Literature 3) of the optical level adjusting device. In an optical level adjusting device 930 illustrated in FIG. 22(a), lights wavelength demultiplexed by a first AWG 931 are inputted to a Mach Zehnder interferometer (MZI) 932 illustrated in FIG. 22(b). The intensities of the lights are adjusted by the MZI 932 and then the lights are multiplexed and outputted by a second AWG 933.
However, the aforementioned wavelength selective optical switch illustrated in FIG. 20 employs four AWGs 911 to 914 and on account of many AWGs being used there is a problem of increasing the size of the entire wavelength selective optical switch 910.
Further, the wavelength selective optical switch illustrated in FIG. 21 employs a single AWG. However, there is a need for connecting the substrate forming the AWG 921 and the respective optical switches 922 through optical fibers, wherein the number of the optical fibers should corresponds to the number of ports, with the result that there occurs the problem of increasing the device size.
Further, the optical level adjusting device 930 illustrated in FIG. 22(a) employs two AWGs 931, 932, with the result that there occurs the problem of increasing the size of the entire optical level adjusting device.
The present invention has been made in view of the aforementioned problems and aims at providing optical devices capable of functioning as a wavelength selective optical switch or optical level adjusting device and enabling reduction in the device size (device scale).
Patent Literature 1
The Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 82, No. 7, pp. 746-752, July 1999
Patent Literature 2
Japanese Patent Laid-Open (Kokai) HEI 8-46569
Patent Literature 3
Japanese Patent Laid-Open (Kokai) 2002-250827